DE102022104418A1 - EDGE EMITTING SEMICONDUCTOR LASER DIODE - Google Patents

Abstract

An edge-emitting semiconductor laser diode is specified, having: - a substrate (1) with a first main area (6) and a second main area (7) opposite the first main area (6), - an epitaxial semiconductor layer stack (2) on the first main area (6 ) of the substrate (1), wherein the epitaxial semiconductor layer stack (2) comprises an active layer (3) for generating electromagnetic radiation, - an adaptation layer (4) which is arranged on the second main surface (7) of the substrate (1), and - an absorption layer (5) which is applied directly to the matching layer (4) and is designed to at least partially absorb the electromagnetic radiation, wherein- the substrate (1) and the matching layer (4) are transparent to electromagnetic radiation generated during operation , and the adaptation layer (4) is set up to increase the absorption of electromagnetic radiation in the absorption layer (5).

Description

An edge-emitting semiconductor laser diode is specified.

An edge-emitting semiconductor laser diode is to be specified which has an improved beam quality. This object is solved by an object having the features of the independent patent claim.

Advantageous embodiments and developments of the edge-emitting semiconductor laser diode are specified in the dependent claims.

In accordance with one embodiment, the edge-emitting semiconductor laser diode has a substrate with a first main area and a second main area lying opposite the first main area. The substrate is, for example, a growth substrate or a carrier substrate. The substrate is set up in particular for mechanical stabilization of the edge-emitting semiconductor laser diode. The main surfaces preferably have a larger surface area than the side surfaces of the substrate.

The substrate has, for example, gallium nitride, sapphire, silicon, silicon carbide or gallium arsenide or consists of one of these materials.

In accordance with a further embodiment, the edge-emitting semiconductor laser diode has an epitaxial semiconductor layer stack on the first main area of the substrate, the epitaxial semiconductor layer stack comprising an active layer for generating electromagnetic radiation. For example, the epitaxial semiconductor layer stack has grown epitaxially on the first main area of the substrate. A main extension plane of layers of the epitaxial semiconductor layer stack is preferably arranged parallel to the first main area of the substrate.

The epitaxial semiconductor layer stack preferably has a III-V compound semiconductor material or consists of a III-V compound semiconductor material. A III/V compound semiconductor material has at least one element from the third main group, such as B, Al, Ga, In, and one element from the fifth main group, such as N, P, As. In particular, the term “III/V compound semiconductor material” includes the group of binary, ternary or quaternary compounds that contain at least one element from the third main group and at least one element from the fifth main group, for example a nitride compound semiconductor material. Nitride compound semiconductor materials are compound semiconductor materials that contain nitrogen, such as the materials from the system In _x Al _y Ga _1-xy N with 0 ≤ x ≤ 1, 0 ≤ y ≤ 1 and x+y ≤ 1.

The active layer preferably comprises a pn junction, a double heterostructure, a single quantum well or particularly preferably a multiple quantum well structure (MQW) for generating radiation. The term quantum well structure does not contain any information about the dimensionality of the quantization. It thus includes, inter alia, quantum wells, quantum wires and quantum dots and any combination of these structures. The active layer is set up, for example, to generate electromagnetic radiation in a spectral range between infrared and ultraviolet light inclusive.

In accordance with a further embodiment of the edge-emitting semiconductor laser diode, the substrate and the epitaxial semiconductor layer stack applied thereto have two opposite facets. The facets are, in particular, side surfaces of the substrate and of the epitaxial semiconductor layer stack and are arranged, for example, perpendicularly or at an angle to the first main surface of the substrate.

A highly reflective layer, which is set up to reflect electromagnetic radiation generated during operation, is preferably arranged on a facet, which is referred to below as the rear side facet. For example, the highly reflective layer reflects at least 90%, preferably at least 99%, of the incident electromagnetic radiation generated during operation.

The facet opposite the rear side facet is referred to below as the light output facet. The light decoupling facet is set up to decouple electromagnetic radiation generated during operation from the edge-emitting laser diode. An anti-reflection layer is preferably arranged on the light coupling-out facet, which has a lower reflectivity than the highly reflective layer on the rear side facet. For example, the anti-reflective layer reflects between 10% and 80% inclusive of operationally generated electromagnetic radiation incident thereon.

The rear side facet and the light coupling-out facet form, in particular, an optical resonator with the layers applied thereon. The optical resonator can also include additional optical elements, such as external mirrors. Generated during operation in the active layer electromagnetic radiation forms a standing electromagnetic wave in the optical resonator.

In connection with the optical resonator, the active layer is set up to generate electromagnetic laser radiation. Electromagnetic laser radiation is created by stimulated emission and, in contrast to electromagnetic radiation that is generated by spontaneous emission, generally has a very long coherence length, a very narrow spectral line width and/or a high degree of polarization.

In accordance with a further embodiment, the edge-emitting semiconductor laser diode has at least one matching layer which is arranged on the second main area of the substrate. For example, the matching layer is applied directly to the second main area of the substrate. The matching layer preferably has a dielectric material or a semiconductor material, or consists of one of these materials. The edge-emitting laser diode can also have a number of matching layers.

In accordance with a further embodiment, the edge-emitting semiconductor laser diode has an absorption layer which is applied directly to the matching layer and is set up to at least partially absorb electromagnetic radiation generated during operation. The absorption layer is preferably applied to a side of the matching layer that faces away from the substrate and completely or partially covers the matching layer. The absorption layer is set up in particular to at least partially absorb electromagnetic laser modes propagating in the substrate. For example, the absorption layer has an absorption coefficient of at least 100 cm ^-1 , preferably at least 1000 cm ^-1 , for electromagnetic radiation generated during operation.

In accordance with a further embodiment of the edge-emitting semiconductor laser diode, the substrate and the matching layer are transparent to electromagnetic radiation generated during operation. In particular, a band gap of the substrate and a band gap of the matching layer are larger than a band gap of the active layer of the epitaxial semiconductor layer stack. For example, the substrate and the matching layer have transmittances for electromagnetic radiation generated during operation of at least 5%, preferably at least 10%, and particularly preferably at least 50%.

In accordance with a further embodiment of the edge-emitting semiconductor laser diode, the adaptation layer is set up to increase the absorption of electromagnetic radiation in the absorption layer. In particular, the adaptation layer is set up to set a phase and a position of intensity maxima of the laser modes propagating in the substrate in such a way that these laser modes experience strong attenuation by the absorption layer. For example, the attenuation of the laser modes propagating in the substrate in an edge-emitting semiconductor laser diode with the matching layer is at least one order of magnitude greater, preferably at least two orders of magnitude higher, than in an otherwise structurally identical edge-emitting semiconductor laser diode without the matching layer.

• - ein Substrat mit einer ersten Hauptfläche und einer der ersten Hauptfläche gegenüberliegenden zweiten Hauptfläche,
• - einen epitaktischen Halbleiterschichtenstapel auf der ersten Hauptfläche des Substrats, wobei der epitaktische Halbleiterschichtenstapel eine aktive Schicht zur Erzeugung elektromagnetischer Strahlung umfasst,
• - eine Anpassschicht, die auf der zweiten Hauptfläche des Substrats angeordnet ist, und
• - eine Absorptionsschicht, die direkt auf der Anpassschicht aufgebracht und dazu eingerichtet ist, die elektromagnetische Strahlung zumindest teilweise zu absorbieren, wobei
• - das Substrat und die Anpassschicht transparent für im Betrieb erzeugte elektromagnetische Strahlung sind, und
• - die Anpassschicht dazu eingerichtet ist, die Absorption von elektromagnetischer Strahlung in der Absorptionsschicht zu erhöhen.

According to a preferred embodiment, the edge-emitting semiconductor laser diode has at least the following features:

• - a substrate having a first main surface and a second main surface opposite the first main surface,
• - an epitaxial semiconductor layer stack on the first main surface of the substrate, wherein the epitaxial semiconductor layer stack comprises an active layer for generating electromagnetic radiation,
• - an adjustment layer arranged on the second main surface of the substrate, and
• - An absorption layer which is applied directly to the matching layer and is set up to at least partially absorb the electromagnetic radiation, wherein
• - the substrate and the matching layer are transparent to electromagnetic radiation generated during operation, and
• - the matching layer is set up to increase the absorption of electromagnetic radiation in the absorption layer.

In edge-emitting semiconductor laser diodes, layers of the epitaxial semiconductor layer stack are arranged in particular in such a way that the electromagnetic radiation generated during operation is guided therein and is coupled out at the light coupling-out facet. For example, the active layer is arranged between two cladding layers that are set up for lateral guidance of the electromagnetic radiation.

Here and below, lateral designates a direction parallel to the first main surface of the substrate.

By scattering at roughness and / or defects and / or due to thin cladding layers, in particular a part of the electromagnetic radiation generated during operation from the Inject semiconductor layer stack into the substrate. Electromagnetic laser modes thus propagate in a transparent substrate, with the substrate being able to act as a waveguide for these laser modes. These electromagnetic laser modes propagating in the substrate, which are also referred to below as substrate modes, can also be coupled out at the light coupling-out facet of the edge-emitting semiconductor laser diode. The substrate modes lead, for example, to additional intensity peaks in a far field of the laser radiation generated during operation. In particular, the substrate modes impair a beam quality and thus an imaging and/or image quality of a laser beam coupled out from the edge-emitting semiconductor laser diode.

The edge-emitting semiconductor laser diode described here is based on the idea of suppressing these substrate modes by applying suitable layers to a main area of the substrate opposite the epitaxial semiconductor layer stack.

For example, substrate modes are at least partially absorbed by the absorption layer. However, strongly absorbing absorption layers, for example metallic absorption layers, can have a high reflectivity. As a result, substrate modes are reflected in particular at the interface with the absorption layer, as a result of which a suppression of substrate modes by the absorption layer can be restricted and/or impeded.

A phase and a position of intensity maxima of the substrate modes are adjusted by the matching layer in particular in such a way that the substrate modes experience strong attenuation by the absorption layer. For example, the attenuation of the substrate modes in a semiconductor laser diode with the matching layer is two orders of magnitude greater than in a semiconductor laser diode that is otherwise structurally identical and without the matching layer. The matching layer is preferably transparent to electromagnetic radiation generated during operation and in particular has a higher refractive index than the substrate. Substrate modes that couple into the matching layer and are reflected at the absorption layer are thus, for example, totally reflected at an interface between the matching layer and the substrate and deflected back in the direction of the absorption layer. As a result, in particular an absorption of electromagnetic radiation in the absorption layer can be increased.

The matching layer, in combination with the absorption layer, enables interfering substrate modes to be suppressed in a simple and cost-effective manner. As a result, in particular the beam quality of the edge-emitting laser diode is increased, as a result of which improved imaging and image quality can be achieved.

In accordance with a further embodiment of the edge-emitting semiconductor laser diode, the substrate is a growth substrate for the epitaxial semiconductor layer stack. In particular, the epitaxial semiconductor layer stack is grown epitaxially on the substrate.

In accordance with a further embodiment of the edge-emitting semiconductor laser diode, the matching layer reduces a distance between the absorption layer and an intensity maximum of electromagnetic laser modes propagating in the substrate. In other words, the adaptation layer is set up to bring the intensity maxima of a multiplicity of electromagnetic laser modes propagating in the substrate closer to the absorption layer. By reducing the distance between the intensity maxima and the absorption layer, the absorption of the laser modes propagating in the substrate is advantageously increased.

This effect of the matching layer is preferably not limited to individual, selected substrate modes. Rather, the matching layer acts on a large part of the electromagnetic laser modes propagating in the substrate.

In accordance with a further embodiment of the edge-emitting semiconductor laser diode, the matching layer reduces reflection at the absorption layer of electromagnetic laser modes propagating in the substrate. This increases in particular an absorption of electromagnetic laser modes propagating in the substrate by the absorption layer. For example, a thickness of the absorption layer is set such that a portion of a plurality of substrate modes reflected at the interface between substrate and matching layer interferes as destructively as possible with a portion of these substrate modes reflected at an interface between matching layer and absorption layer.

According to a further embodiment of the edge-emitting semiconductor laser diode, a refractive index of the matching layer for electromagnetic radiation generated during operation is greater than a refractive index of the substrate for electromagnetic radiation generated during operation. Electromagnetic laser radiation propagating in the substrate can thus be coupled into the matching layer, while electromagnetic laser radiation propagating in the matching layer can in particular be totally reflected at the interface to the substrate. This increases in particular an attenuation of substrate modes by the absorption layer.

For example, the refractive index of the matching layer is at least 0.01 and at most 5 greater than the refractive index of the substrate. The refractive index of the matching layer is preferably at least 0.1 and at most 1.5 greater than the refractive index of the substrate. The refractive index of the matching layer is particularly preferably at least 0.15 and at most 0.7 greater than the refractive index of the substrate.

According to a further embodiment of the edge-emitting semiconductor laser diode, an extinction coefficient of the matching layer for electromagnetic radiation generated during operation is at most 2. The extinction coefficient of the matching layer is preferably at most 0.7 and particularly preferably at most 0.1. The lower the extinction coefficient of the matching layer, the more transparent the matching layer is for electromagnetic radiation generated during operation.

According to a further embodiment of the edge-emitting semiconductor laser diode, a thickness of the matching layer is proportional to a wavelength of electromagnetic radiation generated during operation and inversely proportional to the refractive index of the matching layer for electromagnetic radiation generated during operation. Here and below, the thickness of a layer refers to a spatial extension in a direction perpendicular to the second main area of the substrate.

$\Delta d=\frac{\mathrm{\lambda }}{2\sqrt{n^2-n_{Substrat}^2}}$

und meine ganze Zahl größer oder gleich Null, wobei λ die Wellenlänge im Betrieb erzeugter elektromagnetischer Strahlung, n den Brechungsindex der Anpassschicht für im Betrieb erzeugte elektromagnetische Strahlung und n_Substrat den Brechungsindex des Substrats für im Betrieb erzeugte elektromagnetische Strahlung bezeichnet. Bevorzugt ist m gleich Null und somit D = D₀. Die oben angegebene Formel für die Dicke der Anpassschicht gilt dabei nur für Anpassschichten mit einem Brechungsindex, der größer als ungefähr 2,5 und größer als der Brechungsindex des Substrats ist.According to a further embodiment of the edge-emitting semiconductor laser diode, a thickness of the matching layer is D=D ₀ +m*Δd with a tolerance of ±30 nanometers. there is $D_0=\frac{\mathrm{\lambda }}{450\ast \left(.00192\ast n^2+0.01873\ast n-0.05235\right)},$

$\Delta \mathrm{i.e}=\frac{\mathrm{\lambda }}{2\sqrt{{\mathrm{<figure-callout\; id="2"\; label="n"\; filenames="DE102022104418A1\_0009.png,DE102022104418A1\_0010.png"\; state="\{\{state\}\}">n</figure-callout>}}^2-n_{S\mathrm{and}bst\mathrm{right}a\mathrm{<figure-callout\; id="2"\; label="t"\; filenames="DE102022104418A1\_0009.png,DE102022104418A1\_0010.png"\; state="\{\{state\}\}">t</figure-callout>}}^2}}$

and my integer greater than or equal to zero, where λ is the wavelength of operationally generated electromagnetic radiation, n is the refractive index of the matching layer for operationally generated electromagnetic radiation, and n _substrate is the refractive index of the substrate for operationally generated electromagnetic radiation. m is preferably equal to zero and thus D=D ₀ . The formula given above for the thickness of the matching layer only applies to matching layers with a refractive index that is greater than approximately 2.5 and greater than the refractive index of the substrate.

By choosing the thickness of the matching layer according to the above formula, the attenuation of electromagnetic laser modes propagating in the substrate can be advantageously increased. For example, the thickness of the substrate modes is reduced by three to four orders of magnitude as a result of the matching layer having the thickness specified above, compared to a corresponding edge-emitting semiconductor laser diode without a matching layer.

According to a further embodiment of the edge-emitting semiconductor laser diode, the matching layer has a lateral structuring, so that only part of the second main surface of the substrate is covered by the matching layer and/or the matching layer has at least two separate segments and/or the matching layer has at least one recess. If the matching layer is electrically insulating, lateral structuring of the matching layer is advantageous, in particular for making electrical contact with the epitaxial semiconductor layer stack via the second main area of the substrate.

In accordance with a further embodiment of the edge-emitting semiconductor laser diode, the matching layer has titanium oxide, non-stoichiometric silicon oxide, non-stoichiometric silicon nitride, silicon carbide or gallium phosphide, or consists of one of these materials.

In accordance with a further embodiment, the edge-emitting semiconductor laser diode has at least two matching layers which are arranged between the second main area of the substrate and the absorption layer. The matching layers can have different materials or different material compositions. As a result, damping and thus suppression of electromagnetic laser modes propagating in the substrate can be improved.

In accordance with a further embodiment of the edge-emitting semiconductor laser diode, the matching layer is electrically conductive. Thus, the epitaxial semiconductor layer stack can be electrically contacted in particular via an electrically conductive absorption layer, the electrically conductive matching layer and via an electrically conductive substrate.

In accordance with a further embodiment of the edge-emitting semiconductor laser diode, the absorption layer is set up as a contact layer for making electrical contact with the epitaxial semiconductor layer stack. In particular, the absorption layer is electrically conductive. As a result, process steps in the production of the edge-emitting semiconductor laser diode can be saved and costs can thus be reduced.

According to a further embodiment of the edge-emitting semiconductor laser diode has the Absorption layer on a metal, a semiconductor material or a non-stoichiometric dielectric or consists of one of these materials.

According to a further embodiment, the edge-emitting semiconductor laser diode also has a light blocking layer which is arranged on a partial area of the light output facet of the semiconductor laser diode and is set up to at least partially absorb and/or reflect electromagnetic laser modes propagating in the substrate. The light blocking layer is preferably arranged on a partial area of the light coupling-out facet which comprises the substrate. In particular, the light coupling-out facet remains free of the light-blocking layer in the region of the active layer.

The light-blocking layer can have a plurality of sub-layers or consist of a plurality of sub-layers. For example, a transmission of the light-blocking layer for electromagnetic radiation generated during operation is at most 20%. In particular, the light blocking layer has an oxide, an oxynitride, or a metal, for example aluminum oxide, silicon oxynitride, titanium, platinum or chromium, or consists of one of these materials.

In accordance with a further embodiment, the edge-emitting semiconductor laser diode has a contact layer which is applied to the absorption layer and is set up for making electrical contact with the epitaxial semiconductor layer stack. The contact layer is preferably arranged directly on the absorption layer. The contact layer has a metal, for example, or is formed from a metal. The contact layer is set up for making electrical contact with the epitaxial semiconductor layer stack via the second main area of the substrate.

Alternatively or additionally, the contact layer can also be arranged on the first main area of the substrate. A further contact layer is arranged, for example, on a main area of the epitaxial semiconductor layer stack which is remote from the substrate.

In accordance with a further embodiment of the edge-emitting semiconductor laser diode, the active layer has at least two emission regions which are arranged laterally next to one another and are set up to generate electromagnetic radiation in different wavelength ranges. For example, the emission regions arranged next to one another have different material compositions and thus different band gaps. The emission regions can preferably be electrically contacted independently of one another and can therefore be operated and/or controlled independently of one another. The emission regions of the active layer arranged next to one another can also generate electromagnetic radiation in the same wavelength range. For example, the edge-emitting semiconductor laser diode is designed as a laser bar.

According to a further embodiment of the edge-emitting semiconductor laser diode, the matching layer has at least two partial regions arranged laterally next to one another, one partial region being arranged below an emission region in a direction perpendicular to the first main area of the substrate. In particular, each emission region of the active layer has an associated portion of the matching layer on the opposite main surface of the substrate. In this case, the partial areas of the matching layer can be connected to one another or spatially separated from one another.

According to a further embodiment of the edge-emitting semiconductor laser diode, the partial areas of the matching layer have different materials and/or different thicknesses. In the event that the active layer has a plurality of emission regions that are designed to generate electromagnetic radiation in different wavelength ranges, the thickness of the matching layer in the different partial regions can be selected to match an emitter wavelength of the individual emission regions.

• 1 und 2 zeigen Profile elektromagnetischer Laserstrahlung im Fernfeld einer kantenemittierenden Halbleiterlaserdiode.
• 3, 4 und 5 zeigen verschiedene schematische Darstellungen einer kantenemittierenden Halbleiterlaserdiode gemäß einem Ausführungsbeispiel.
• 6 und 7 zeigen schematische Darstellungen einer Modenstärke von Substratmoden als Funktion einer Dicke der Anpassschicht.
• 8 zeigt eine schematische Darstellung einer Dicke der Anpassschicht als Funktion eines Brechungsindex der Anpassschicht.
• 9 zeigt eine schematische Darstellung einer Modenstärke von Substratmoden als Funktion eines Brechungsindex der Anpassschicht.
• 10 zeigt eine schematische Darstellung einer Modenstärke von Substratmoden als Funktion eines Extinktionskoeffizienten der Anpassschicht.
• 11 bis 15 zeigen schematische Schnittdarstellungen von kantenemittierenden Halbleiterlaserdioden gemäß weiterer Ausführungsbeispiele.
• 16 bis 23 zeigen schematische Draufsichten auf die zweite Hauptfläche des Substrats von kantenemittierenden Halbleiterlaserdioden gemäß verschiedener Ausführungsbeispiele.
• 24 bis 26 zeigen schematische Schnittdarstellungen von kantenemittierenden Halbleiterlaserdioden gemäß weiterer Ausführungsbeispiele.
• 27 zeigt eine schematische Darstellung der Intensität von Substratmoden gemäß einem Ausführungsbeispiel.

Further advantageous embodiments and developments of the edge-emitting semiconductor laser diode result from the exemplary embodiments described below in connection with the figures.

• 1 and 2 show profiles of electromagnetic laser radiation in the far field of an edge-emitting semiconductor laser diode.
• 3 , 4 and 5 show various schematic representations of an edge emitting semiconductor laser diode according to an embodiment.
• 6 and 7 show schematic representations of a mode strength of substrate modes as a function of a thickness of the matching layer.
• 8th shows a schematic representation of a thickness of the matching layer as a function of a refractive index of the matching layer.
• 9 shows a schematic representation of a mode strength of substrate modes as a function of a refractive index of the matching layer.
• 10 shows a schematic representation of a mode strength of substrate modes as Function of an extinction coefficient of the matching layer.
• 11 until 15 show schematic sectional representations of edge-emitting semiconductor laser diodes according to further exemplary embodiments.
• 16 until 23 show schematic plan views of the second main area of the substrate of edge-emitting semiconductor laser diodes according to various exemplary embodiments.
• 24 until 26 show schematic sectional representations of edge-emitting semiconductor laser diodes according to further exemplary embodiments.
• 27 FIG. 12 shows a schematic representation of the intensity of substrate modes according to an embodiment.

Elements that are the same, of the same type or have the same effect are provided with the same reference symbols in the figures. The figures and the relative sizes of the elements shown in the figures are not to be regarded as being to scale. Rather, individual elements, in particular layer thicknesses, can be shown in an exaggerated size for better representation and/or for better understanding.

1 shows a cross section of the laser beam decoupled from the edge emitting laser diode. The electromagnetic laser radiation has in particular a Gaussian mode profile 20 with different mode widths in two mutually orthogonal directions. The area marked with an ellipse shows additional structures in the decoupled laser beam, which are caused by electromagnetic laser modes 9 propagating in the substrate 1 . These substrate modes 9 are at least partially decoupled from the edge-emitting semiconductor laser diode, impair the beam quality and lead to poorer imaging quality, for example.

2 shows a mode profile 20 of electromagnetic laser radiation in the far field of an edge-emitting semiconductor laser diode, the intensity I of the electromagnetic laser radiation being shown as a function of an emission angle α. The electromagnetic laser radiation has, in particular, a Gaussian mode profile 20 . Furthermore, the mode profile 20 shows additional intensity peaks 24 of the electromagnetic laser radiation, which are caused by electromagnetic laser modes 9 propagating in the substrate 1, which are coupled out by the edge-emitting semiconductor laser diode. The edge-emitting semiconductor laser diode described here is based on the idea of largely suppressing these additional intensity peaks 24 .

The edge emitting semiconductor laser diode according to the embodiment of 3 has a substrate 1 with an epitaxial semiconductor layer stack 2 applied thereto. The epitaxial semiconductor layer stack 2 is applied to a first main surface 6 of the substrate 1 and has a nitride compound semiconductor material, for example. The epitaxial semiconductor layer stack 2 includes an active layer 3 for generating electromagnetic radiation. Furthermore, the epitaxial semiconductor layer stack 2 has cladding layers 10 for guiding the electromagnetic laser radiation generated during operation in the active layer 3 , with the active layer 3 being arranged between two cladding layers 10 .

The substrate 1 is in particular a growth substrate on which the epitaxial semiconductor layer stack 2 has grown epitaxially. For example, the substrate 1 has gallium nitride or silicon carbide or consists of one of these materials. The substrate 1 is transparent to electromagnetic laser radiation generated during operation. In particular, the substrate 1 has a larger band gap than the active layer 3 of the epitaxial semiconductor layer stack 2. Electromagnetic laser radiation generated during operation can thus be coupled at least partially from the active layer 3 into the transparent substrate 1 and propagate in the substrate 1 as an electromagnetic laser mode 9.

An adaptation layer 4 is applied directly to the second main surface 7 of the substrate 1 . The matching layer 4 has a dielectric material or a semiconductor material that is transparent to electromagnetic radiation generated during operation. For example, the matching layer 4 has gallium phosphide or consists of gallium phosphide. In particular, a refractive index n of the matching layer 4 for electromagnetic radiation generated during operation is greater than a refractive index of the substrate 1. For example, the refractive index n of the matching layer 4 is at least 0.15 and at most 0.7 greater than the refractive index of the substrate 1. Des Furthermore, the extinction coefficient k of the matching layer is preferably at most 0.1.

An absorption layer 5 is applied directly to the main surface of the matching layer 4 opposite the substrate 1 . The absorption layer 5 has in particular a high absorption coefficient for electromagnetic radiation generated during operation and is formed from a metal, for example.

A thickness D of the matching layer 4 is selected in such a way that substrate modes 9 are absorbed as strongly as possible by the absorption layer 5 and are thereby damped. For example, the matching layer 4 reduces a reflection of substrate modes 9 at the absorption layer 5. The thickness D of the matching layer 4 is in particular proportional to the wavelength of electromagnetic radiation generated during operation and inversely proportional to a refractive index n of the matching layer.

A contact layer 19 for electrically contacting the active layer 3 is arranged on a main surface of the epitaxial semiconductor layer stack 2 opposite the substrate 1 . Furthermore, the absorption layer 5 is set up as a further contact layer for making electrical contact with the active layer 3, with the substrate 1 being electrically conductive. For example, the substrate has a doped semiconductor material. The adaptation layer 4 arranged between the substrate 1 and the absorption layer 5 is either electrically conductive or has a lateral structuring 11 . Examples of lateral structuring 11 of the matching layer 4 are in the 16 until 23 shown. Due to the lateral structuring 11 of the matching layer 4, the edge-emitting semiconductor laser diode has, in particular, a direct, electrically conductive connection between the absorption layer 5 and the substrate 1.

Opposite side faces of the semiconductor laser diode are formed as a light output facet 15 and rear side facet 18, which together form an optical resonator of the edge-emitting semiconductor laser diode. In connection with the active layer 3, the optical resonator is set up to generate electromagnetic laser radiation during operation. The electromagnetic laser radiation is coupled out via the light coupling-out facet 15 and emitted by the edge-emitting semiconductor laser diode at the emission angle α. In this case, the emission angle α designates an angle between a surface normal of the light decoupling facet 15 and an emission direction of the electromagnetic laser radiation generated during operation.

4 shows a schematic perspective view of the edge emitting semiconductor laser diode according to the embodiment of FIG 3 . The epitaxial semiconductor layer stack 2 has, in particular, a ridge waveguide 22 for guiding electromagnetic radiation generated during operation. The ridge waveguide 22 extends in the lateral direction between the light coupling-out facet 15 and the opposite rear side facet 18. The contact layer 19 for electrically contacting the active layer 3 covers the ridge waveguide 22 completely.

The matching layer 4 covers the second main area 7 of the substrate 1 only partially. In particular, a region of the second main surface 7 is covered by the matching layer 4 in the vertical direction above the ridge waveguide 22 . The matching layer 4 covers a region of the second main surface 7 which, in the lateral direction perpendicular to a main extension direction of the ridge waveguide 22, preferably extends beyond the ridge waveguide 22 by at least 30 micrometers, particularly preferably by at least 60 micrometers. Regions of the second main surface 7 that are not covered by the matching layer 4 are covered by the absorption layer 5 that extends over the entire second main surface 7 . The absorption layer 5 is thus set up in direct electrical contact with the electrically conductive substrate 1 and for making electrical contact with the semiconductor layer stack 2 .

5 shows a schematic sectional view of the edge emitting semiconductor laser diode according to the embodiment of FIG 3 in a plan view of the light output facet 15. In particular, the matching layer 4 does not completely cover the second main surface 7 of the substrate 1, but protrudes in the lateral direction on both sides by at least 30 micrometers beyond the ridge waveguide 22.

6 1 schematically shows a dependency between a thickness D of the matching layer 4 and a mode strength S of the substrate modes 9. The mode strength S indicates in particular a relative intensity of the substrate modes 9 coupled out of the semiconductor laser diode. A mode strength S with the value S=1 corresponds to a semiconductor laser diode without an absorption layer 5 and is in 4 marked with an asterisk. In contrast, a structurally identical semiconductor laser diode with an additional absorption layer 5, but without a matching layer 4, has a lower mode strength S, which is 4 marked with a square.

Furthermore shows 4 shows the mode strength S of substrate modes 9 of a semiconductor laser diode with an absorption layer 5 and a matching layer 4 as a function of the thickness D of the matching layer 4. In particular 4 that the mode strength S of the substrate modes 9 can be reduced by a suitable choice of the thickness D of the matching layer 4, for example by two orders of magnitude.

$$

ist und m eine ganze Zahl größer gleich Null ist.
Dabei bezeichnen n und n_Substrat Brechungsindizes der Anpassschicht 4 und des Substrats 1 für im Betrieb erzeugte elektromagnetische Strahlung. 7 shows the results of a numerical simulation of the mode strength S of substrate modes 9 as a function of the thickness D of the matching layer 4. The mode strength S has a plurality of minima 21 that occur approximately periodically. The first minimum 21 occurs at a thickness D of the matching layer 4 denoted by D ₀ . More minima 21 step approximately at thicknesses D=D ₀ +m*Δd of the matching layer 4, where $\Delta \mathrm{i.e}=\frac{\mathrm{\lambda }}{2\sqrt{{\mathrm{<figure-callout\; id="2"\; label="n"\; filenames="DE102022104418A1\_0009.png,DE102022104418A1\_0010.png"\; state="\{\{state\}\}">n</figure-callout>}}^2-n_{S\mathrm{and}bst\mathrm{right}a\mathrm{<figure-callout\; id="2"\; label="t"\; filenames="DE102022104418A1\_0009.png,DE102022104418A1\_0010.png"\; state="\{\{state\}\}">t</figure-callout>}}^2}}$

$$

and m is an integer greater than or equal to zero.
In this case, n and n _substrate denote refractive indices of the matching layer 4 and of the substrate 1 for electromagnetic radiation generated during operation.

parametrisieren, wobei λ die Wellenlänge im Betrieb erzeugter elektromagnetischer Strahlung und n den Brechungsindex der Anpassschicht 4 bezeichnet. 8th shows the thickness D ₀ at which the first minimum 21 of the mode strength S in 5 occurs as a function of the refractive index n of the matching layer 4. The thickness D ₀ can be approximated by the function $D_0=\frac{\mathrm{\lambda }}{450\ast \left(.00192\ast n^2+0.01873\ast n-0.05235\right)},$

parameterize, where λ denotes the wavelength of electromagnetic radiation generated during operation and n denotes the refractive index of the matching layer 4 .

9 shows numerical results for the mode strength S of substrate modes 9 as a function of the refractive index n of the matching layer 4. The thickness D of the matching layer 4 and the optical properties of the absorption layer 5 are fixed. In particular shows 7 that the mode strength S of the substrate modes 9 has a strongly pronounced minimum 21 at a specific value of the refractive index n of the matching layer 4 . This value depends, among other things, on the optical properties of the absorption layer 5, in particular on the complex refractive index of the absorption layer 5.

10 shows a mode strength S of substrate modes 9 as a function of an extinction coefficient k of the matching layer 4. The thickness D and the refractive index n of the matching layer 4, as well as optical properties of the absorption layer 5, are fixed. In particular shows 8th that the smallest possible extinction coefficient k of the matching layer 4 results in a particularly low mode strength S of the substrate modes 9 . In other words, the smallest possible extinction coefficient k of the matching layer 4 leads to an advantageously large damping of the substrate modes 9.

The edge emitting semiconductor laser diode according to the embodiment of 11 has in contrast to the semiconductor laser diode 3 a plurality of matching layers 4 which are arranged between the substrate 1 and the absorption layer 5 . The various matching layers 4 have, for example, different materials and thus different optical properties, in particular different refractive indices n. As a result, the damping of the substrate modes 9 can be set more precisely and thus improved.

The edge emitting semiconductor laser diode according to the embodiment of 12 points compared to the semiconductor laser diode in 3 additionally a light blocking layer 14 . The light-blocking layer 14 partially covers the light-coupling facet 15, in particular in the region of the substrate 1. The light-blocking layer 14 is set up for at least partial absorption and/or reflection of substrate modes 9. This at least partially reduces or prevents substrate modes 9 from being coupled out of the semiconductor laser diode. In conjunction with the matching layer 4 and the absorption layer 5, substrate modes 9 in the far field of the laser radiation coupled out by the semiconductor laser diode can be suppressed even more as a result.

The embodiment in 13 has in contrast to the edge-emitting semiconductor laser diode 5 an adaptation layer 4 which completely covers the second main surface 7 of the substrate 1 . The matching layer 4 is electrically conductive in order to ensure electrical contact between the absorption layer 5 and the epitaxial semiconductor layer stack 2 via the electrically conductive substrate 1 .

In contrast to the edge-emitting semiconductor laser diode in 13 is in the embodiment of the edge emitting semiconductor laser diode in 14 the absorption layer 5 is not set up as a contact layer. Thus, no electrically conductive matching layer 4 and no electrically conductive substrate 1 are necessary for making electrical contact with the epitaxial semiconductor layer stack 2 . Instead, the contact layers 19 for making electrical contact with the epitaxial semiconductor layer stack 2 are arranged parallel to the ridge waveguide 22 and laterally spaced from the epitaxial semiconductor layer stack 2 on the first main surface 6 of the substrate 1 and on the main surface of the epitaxial semiconductor layer stack 2 facing away from the substrate 1.

In the edge emitting semiconductor laser diode according to the embodiment in 15 an area where the absorption layer 5 is in direct contact with the second main surface 7 of the substrate 1 is larger than that of the edge-emitting semiconductor laser diode in FIG 12 . As a result, in the case of a non-electrically conductive matching layer 4, electrical contact between the absorption layer 5 and the substrate 1 can be improved.

16 shows a plan view of the second main surface 7 of the substrate 1 of an edge-emitting semiconductor laser diode. In this case, the second main surface 7 is partially free of the matching layer 4 , while the absorption layer 5 extends over the entire second main surface 7 . In particular, an area at the edge of the second major surface 7, which extends between the light output facet 15 and the rear side facet 18, free of the matching layer 4.

In the case of the edge-emitting semiconductor laser diode in 17 are in contrast to 16 two areas on opposite edges of the second main surface 7 free of the matching layer 4.

In 18 covers the absorption layer 5 in contrast to 17 the substrate 1 is not complete. However, the matching layer 4 is completely covered by the absorption layer 5 .

In 19 are the matching layer 4 and the absorption layer 5 in contrast to 18 laterally spaced from the light output facet 15 and the rear facet 18 .

In contrast to the edge-emitting semiconductor diode in 19 has the matching layer 4 in 20 an additional lateral structuring 11 on. In particular, the adaptation layer 4 has a multiplicity of segments 12 which are separated from one another and which are arranged along a direction between the light coupling-out facet 15 and the rear-side facet 18 .

In the case of the edge-emitting semiconductor laser diode in 21 is compared to 17 only a partial area of the second main surface 7 at the light coupling-out facet 18 is covered by the adaptation layer 4 .

The edge-emitting semiconductor laser diode in 22 has in contrast to the edge-emitting semiconductor laser diode 20 a lateral structuring 11 of the matching layer 4 in the form of a multiplicity of recesses 13 .

The edge-emitting semiconductor laser diode in 23 has an absorption layer 5 which comprises two segments 12 separated from one another. The two segments 12 are arranged in the vicinity of the light coupling-out facet 15 and the rear side facet, while the adaptation layer 4 covers an area of the second main surface 7 adjoining the light coupling-out facet 15 .

24 FIG. 1 shows a plan view of the light output facet 15 of an edge-emitting semiconductor laser diode. The epitaxial semiconductor layer stack 2 has three emission regions 16 which are laterally spaced apart from one another. The three emission regions 16 are electrically contacted independently of one another by contact layers 19 that are separate from one another and can therefore be controlled and/or operated independently of one another. For each emission region 16, an associated partial region 17 of the matching layer 4 and the absorption layer 5 is applied to the second main surface 7 of the substrate 1, which is arranged directly opposite the respective emission region 16.

The partial areas 17 of the matching layer 4 in the edge-emitting semiconductor laser diode in FIG 25 point in contrast to 24 different properties. For example, the matching layer 4 has different thicknesses D and/or different material compositions in the subregions 17 . Thus, the adaptation layer 4 can be adapted to different emission wavelengths of the different emission regions 16 in the partial regions 17, for example.

26 shows an edge-emitting semiconductor laser diode, in contrast to 24 has a coherent matching layer 4 . In particular, the matching layer 4 is not divided into partial regions 17 that are separate from one another. All emission regions 16 of the semiconductor layer stack 2 thus share a common matching layer 4.

27 shows a schematic representation of an intensity I of substrate modes 9 in a direction R perpendicular to the second main surface 7 of the substrate 1. The substrate modes 9 are represented in this direction R as standing electromagnetic waves. At the interface between the matching layer 4 and the metallic absorption layer 5, the substrate modes 9 have, in particular, a node at which the intensity I of the substrate modes 9 disappears. The intensity maxima 23 of the substrate modes 9 are moved closer to the absorption layer 5 by the matching layer 4 . An attenuation of the substrate modes 9 by the absorption layer 5 is thus advantageously increased.

The invention is not limited to these by the description based on the exemplary embodiments. Rather, the invention encompasses every new feature and every combination of features, which in particular includes every combination of features in the patent claims, even if this feature or this combination itself is not explicitly specified in the patent claims or exemplary embodiments.

Reference List

1

substrate

2

epitaxial semiconductor layer stack

3

active layer

4

matching layer

5

absorption layer

6

first main surface

7

second main surface

8th

Distance

9

substrate mode

10

coat layer

11

structuring

12

segment

13

recess

14

light block layer

15

light extraction facet

16

emission range

17

subarea

18

back facet

19

contact layer

20

fashion profile

21

minimum

22

ridge waveguide

23

maximum intensity

24

peak intensity

I

intensity

S

mode strength

n

refractive index

k

extinction coefficient

D

thickness

a

beam angle

R

Direction

Claims (17)

Edge emitting semiconductor laser diode, comprising: - a substrate (1) having a first main surface (6) and a second main surface (7) opposite the first main surface (6), - an epitaxial semiconductor layer stack (2) on the first main surface (6) of the substrate (1), wherein the epitaxial semiconductor layer stack (2) comprises an active layer (3) for generating electromagnetic radiation, - At least one matching layer (4) which is arranged on the second main surface (7) of the substrate (1), and - An absorption layer (5) which is applied directly to the matching layer (4) and is set up to at least partially absorb the electromagnetic radiation, wherein - the substrate (1) and the matching layer (4) are transparent to electromagnetic radiation generated during operation, and - The matching layer (4) is set up to increase the absorption of electromagnetic radiation in the absorption layer (5). Edge-emitting semiconductor laser diode according to the preceding claim, wherein the substrate (1) is a growth substrate for the epitaxial semiconductor layer stack (2). Edge-emitting semiconductor laser diode according to one of the preceding claims, wherein the matching layer (4) reduces a distance (8) between the absorption layer (5) and an intensity maximum (23) of electromagnetic laser modes (9) propagating in the substrate (1). Edge-emitting semiconductor laser diode according to one of the preceding claims, wherein the matching layer (4) reduces a reflection of electromagnetic laser modes (9) propagating in the substrate (1) at the absorption layer (5). Edge-emitting semiconductor laser diode according to one of the preceding claims, wherein a refractive index (n) of the matching layer (4) for electromagnetic radiation generated during operation is greater than a refractive index of the substrate (1) for electromagnetic radiation generated during operation. Edge-emitting semiconductor laser diode according to one of the preceding claims, wherein an extinction coefficient (k) of the matching layer (4) for electromagnetic radiation generated during operation is at most 2. Edge-emitting semiconductor laser diode according to one of the preceding claims, wherein a thickness (D) of the matching layer (4) is proportional to a wavelength of electromagnetic radiation generated during operation and inversely proportional to a refractive index (n) of the matching layer (4) for electromagnetic radiation generated during operation. Edge-emitting semiconductor laser diode according to one of the preceding claims, wherein a thickness (D) of the matching layer (4) is D = D ₀ + m * Δd with a tolerance of ±30 nanometers, wherein $D_0=\frac{\mathrm{\lambda }}{450\ast \left(.00192\ast n^2+0.01873\ast n-0.05235\right)},$

$\Delta \mathrm{i.e}=\frac{\mathrm{\lambda }}{2\sqrt{n^2-n_{S\mathrm{and}bst\mathrm{right}at}^2}},$

m is an integer greater than or equal to zero, λ is a wavelength of electromagnetic radiation generated during operation, n is a refractive index of the matching layer (4) for electromagnetic radiation generated during operation and n _substrate is a refractive index of the substrate (1) for electromagnetic radiation generated during operation. Edge-emitting semiconductor laser diode according to one of the preceding claims, wherein the matching layer (4) has a lateral structuring (11) so that only part of the second main surface (7) of the substrate is covered by the matching layer and/or the matching layer (4) has at least two has separate segments (12) and/or the adaptation layer (4) has at least one recess (13). Edge-emitting semiconductor laser diode according to one of the preceding claims, in which the matching layer (4) has titanium oxide, non-stoichiometric silicon oxide, non-stoichiometric silicon nitride, silicon carbide or gallium phosphide. Edge-emitting semiconductor laser diode according to one of the preceding claims, wherein the matching layer (4) is electrically conductive. Edge-emitting semiconductor laser diode according to one of the preceding claims, the absorption layer (5) being set up as a contact layer (19) for making electrical contact with the epitaxial semiconductor layer stack (2). Edge-emitting semiconductor laser diode according to one of the preceding claims, in which the absorption layer (5) has a metal, a semiconductor material or a non-stoichiometric dielectric. Edge-emitting semiconductor laser diode according to one of the preceding claims, additionally having a light blocking layer (14) which is arranged on a partial area of a light coupling-out facet (15) of the semiconductor laser diode and is set up to at least partially absorb and/or at least partially absorb electromagnetic laser modes (9) propagating in the substrate (1). or to reflect. Edge-emitting semiconductor laser diode according to one of the preceding claims, wherein the active layer (3) has at least two emission regions (16) which are arranged laterally next to one another and are set up for generating electromagnetic radiation in different wavelength ranges. Edge-emitting semiconductor laser diode according to the preceding claim, in which the matching layer (4) has at least two partial regions (17) arranged laterally next to one another and in each case one partial region (17) in a direction perpendicular to the first main surface (6) of the substrate (1) below an emission region ( 16) is arranged. Edge-emitting semiconductor laser diode according to the preceding claim, wherein the partial regions (17) of the matching layer (4) have different materials and/or different thicknesses (D).

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